Historical trends in the production of the semiconductor integrated circuits have been to increase device density at lower cost per circuit, and at high yield. Opportunities now exist to substantially improve the availability, reliability, and performance of semiconductor devices while simultaneously reducing manufacturing cycle time, reducing thermal budgets, and increasing product yields. It is believed that these benefits will, in the future, be largely realized by adopting technology for the sensing and control of processing steps in the manufacturing of semiconductor devices. The benefits of closed loop control, compared to fixed set point control, are summarized below:
______________________________________ Sensor Driven Closed Loop Control Fixed Set Point Control ______________________________________ Immediate measurements on every wafer Delayed measurements No extra wafer handling Sporadic measurements Automatic closed loop control Extra wafer handling Potential Overall Equipment Effectiveness Operator required (OEE) about 57% OEE about 30% Tighter product specification Looser specifications ______________________________________
In current practice, fixed set point control is typically used for process steps, with reactor recipes being set so that a parameter value matches a target specification. As illustrated in appended FIG. 1(a), the process is run until the parameter value (as determined by measurements on one in 25 or one in 50 wafers) is outside preset limits, at which time the process is stopped and the reactor is retuned. This practice results in substantial down-time for process retuning, the productions of substantial amounts of scrapped material before the process is stopped, and substantially wider variations in the product specifications than necessary.